This invention relates generally to the retorting of high molecular weight organic materials, and more particularly to such retorting processes that provide high liquid yields.
Oil shale is a sedimentary rock that contains a solid and combustible organic matter, called kerogen, within a mineral matrix. Kerogen is a high molecular weight organic material whose composition is indefinite in that it significantly varies from deposit to deposit. Although it is largely insoluble in petroleum solvents, when kerogen is heated, or pyrolyzed, it decomposes to yield some liquid shale oil, the amount strongly depending on the conditions under which the pyrolysis is carried out. The present invention involves the aboveground processing of oil shale, wherein the shale is mined, crushed, and then pyrolyzed to produce shale oil.
For shale oil production to be economical, the retort processing of the oil shale is very preferably continuous. Generally speaking, continuous retorts may be heated by burning the residual organic matter of spent oil shale within the retort, or heated by preheating various materials, such as spent shale, gas, sand, rocks or even ceramic balls, in an exterior furnace that is sometimes separately supplied with fuel, and then circulating the preheated material through the retort. It is presently believed that the thermal conversion of kerogen to liquid shale oil is best achieved via the rapid heating provided by solid-to-solid heat transfer techniques. These processes can be carried out at low temperatures and near ambient pressures, and often utilize fluidized bed retort vessels somewhat similar to those used for catalytic cracking by the petroleum industry. Even though it is very convenient to use burnt oil shale for heat transfer, heating via a more inert solid can often result in the production of more shale oil.
Various catalysts are sometimes used in oil shale processing. Hydrocarbon cracking catalysts are used in various phases of shale oil upgrading. These catalysts, which are typically clays, modified clays, or zeolites, are believed to interact with volitile hydrocarbons to effect the scission, or breaking, of carbon-to-carbon bonds, or to initiate other molecular rearrangements. However, cracking catalysts are not presently used to improve yields in the oil shale retorting process.
Tar sands are high molecular weight organic materials that are defined herein as sands that are fully or partially saturated by oil or bitumen.
Solvent refined coal is a high molecular weight organic material that is defined herein as the solid product from a coal processing plant that uses solvent refining to beneficiate coal. A very well known solvent refined coal plant is the SRCl plant located at Wilsonville, Alabama.
Petroleum residua are high molecular weight organic materials defined herein as the material that remains after the complete distillation of crude oil, crude oil products, or partially refined crude oils.
Polyethylenes are high molecular weight organic materials that are polymers of ethylene, and comprise a form of light, tough, thermoplastic synthetic resins. Polyethylenes frequently contain minor additives or other incorporated monomers.
Polystyrene is a high molecular weight organic material that is a polymer of styrene in its various forms and modifications.
Heavy oil is a term used in the petroleum industry for non-volatile oils.
Bitumens are any of a number of inflammable mineral substances consisting mainly of hydrocarbons, including the hard, brittle varieties of asphalt, the semisolid maltha, and mineral tars.
Pure rubber is a hydrocarbon having the composition C.sub.5 H.sub.8).sub.x, that is often altered by vulcanization and the addition of additives to give it various desired properties. Synthetic rubber may be any of various artificial substances that more or less closely resemble natural rubber and, especially, may be made by the polymerization of unsaturated hydrocarbons such as butadiene, isoprene, dimethyl-butadiene, and the like.
Goldstein, in U.S. Pat. No. 4,078,991 issued Mar. 14, 1978, teaches a method for treating clay materials, such as montmorillonite, to prepare a super-active catalyst for use in the catalytic upgrading of organic materials, such as heavy crude petroleum stock and mineral-free kerogen, at temperatures below about 250 degrees centigrade.
Wunderlich et al, in U.S. Pat. No. 3,844,929 issued Oct. 29, 1974, disclose the retorting of crushed oil shale by tumbling the shale with hot special heat-carrying pellets.
Krebs, in U.S. Pat. No. 2,627,499 issued Feb. 3, 1953, teaches the catalytic distillation of oil shale in a fluidized mass, wherein a finely divided conventional cracking catalyst has a particle size substantially larger than the particle size of the oil-bearing mineral during the distillation process.
Shabtai, in U.S. Pat. No. 4,238,364 issued Dec. 9, 1980, discusses types of molecular sieve cracking catalysts that consist of acidic forms of partially cross-linked smectites, and that include ions of hydrogen and rare-earth elements.
The size of the oil shale deposits of the world is enormous. Even though the potential of this shale is great, commercial production of shale oil has generally been considered uneconomic. Presently, there is virtually no commercial production of shale oil in the United States. It is, therefore, quite obvious that there is currently an urgent need for oil shale retorting processes that will provide enhanced yields of liquid product. There is a similar need for liquid product retorting processes for organic materials such as tar sands, solvent refined coal, petroleum residua, polyethylene, polystyrene, heavy oil, bitumen, and rubber wastes.